1. Field of the Invention
The present invention relates to a power control method for a wireless local loop (hereinafter, “WLL”), and more particularly, to a reverse power control method of packet data transmission for a WLL.
2. Background of the Related Art
A WLL system is a system which replaces a predetermined portion of a wire communication line between a conventional switching network or public switching telephone network (PSTN) and a general subscriber network by a wireless line. Wire communication techniques adapted to the WLL include using an artificial satellite, using microwaves, using cellular techniques, using the cordless method, and using the WCDMA method.
FIG. 1 is a block diagram of a related art WLL system configuration. The WLL system as illustrated in FIG. 1 includes a plurality of subscriber terminals 10 used for communication by each subscriber and a plurality of radio interface units 20 (hereinafter, “RIU”) coupled with the plurality of subscriber terminals 10 by a wire interface. Each of the plurality of RIUs 20 is also connected with a radio port 30 (hereinafter “RP”) by a wireless interface, which provides a relay between both sides. The plurality of RPs 30 are wirelessly coupled with the plurality of RIUs for connecting or disconnecting a bearer. Next, radio port controllers 40 (hereinafter “RPC”) are wirelessly connected with the plurality of RPs 30 for linking the subscriber of the WLL with a subscriber of another communication network by a call link. Finally, a network management system 50 (hereinafter, “NMS”) is coupled to the RPC 40 for operating, controlling, maintaining, and repairing the entire WLL system.
FIG. 2 is a block diagram showing additional detail of the RP 30 and the RIU 20. Referring to FIG. 2, the RIU 20 includes an amplifier 22 for amplifying a source data applied from the subscriber terminal 10 to output the same and a first transmitter 24 for modulating a signal outputted from the amplifier 22 into a high frequency to wirelessly transmit the same. It further includes a first receiver 26 for receiving a high frequency signal wirelessly transmitted from the RP 30 and a first demodulator 28 for demodulating the high frequency signal from the first receiver 26 to extract a data.
The RP 30 includes a second receiver 32 for receiving the high frequency signal sent from the RIU 20 and a second demodulator 34 for demodulating the high frequency signal from the second receiver 34 to extract a data. Next, it includes a comparator 35 for comparing a received power value Eb transmitted from the second demodulator 34 with a prescribed reference power value No and calculating a ratio from them. The RP 30 further includes a SELECTOR 36 for mixing a signal controlling the power of the RIU 20 with a transmission data and a second transmitter 38 for modulating a signal outputted from the SELECTOR 36 into a high frequency signal.
In the WLL, the RIUs 20 in the same service area must transmit data at the same power level.
For example, if one of the plurality of RIUs 20 connected with the RP 30 has a relatively high power, this causes an interruption of the other RIUs 20, thereby increasing the framed error rate (FER) of a data. In addition, a call quality is reduced, and accordingly the other RIUs 20 must increase their power competitively in order to maintain their call quality. As a result, the efficiency of the WLL system is reduced. The corresponding RP 30 cannot recognize signal transmission of the corresponding RIU 20 if the power of the RIU 20 is relatively low.
Due to this problem, a method for appropriately controlling the power of the RIU 20 is needed.
FIG. 3 is a view of a related art power control status of a WLL. As illustrated in FIG. 3, the related art RP 30 measures the power of the RIU 20 in 1.25 ms duration, and the NMS 50 monitors and controls the operation of the above reverse power control.
FIG. 4 illustrates a sequential view of the related art reverse power control operation of the WLL.
The operational process of the reverse power control of the WLL in the conventional art includes a first step S10, in which the RP 30 initializes a timer T in order to measure the power outputted from the RIU 20 at a predetermined time interval, for instance, in 1.25 ms duration. Next, in step S20, the timer initialized in step S10 counts up and in step 30, it is determined whether power measuring time (1.25 ms) has passed by the timer in step S20. In step S40, feedback is sent to the count up of step S20 if the power, measuring time (1.25 ms) has not passed by the timer in step S20. Alternatively, if it is determined in step 30 that the measuring time (1.25 ms) has passed, the process proceeds to step S40, where it calculates the following equation 1:Pm=Eb/No  [Equation 1]
Here, Pm is the calculating value, Eb is the received output value, and No is the reference output value.
Next, in step S50, the RP 30 compares a calculated value of Pm with a preset reference value Pr. Then, in a step S60, the power of the RIU 20 is controlled to be down-adjusted by 0.5 dB if the calculating value Pm is larger than the reference value Pr. Alternatively, in step S70, the power of the RIU 20 is controlled to be up-adjusted by 0.5 dB if Pm is not greater than Pr.
As described above, in the related art reverse power control method for a WLL has various problems. For example, since the RP 30 transmits a power control signal continuously to the RIU 20 at predetermined time intervals, much power is consumed and the load of the network system is increased.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.